Conventionally, there has been a cutting insert for rotary cutting, as described in, for example, Patent Document 1. The cutting insert in Patent Document 1 includes two opposing end surfaces, a peripheral side surface extending between these end surfaces, and a plurality of cutting edges extending on an intersecting edge between each of the two end surfaces and the peripheral side surface. Each cutting edge includes a corner cutting edge extending at a certain corner of the relevant end surface, a major cutting edge extending from the corner cutting edge toward an adjacent corner, and a minor cutting edge extending from a side, different from the major cutting edge, of the corner cutting edge. When a plane passing through a middle part between the two end surfaces and extends so as to intersect with the peripheral side surface is defined as a middle plane, the major cutting edge is inclined so as to approach the middle plane as the distance from the adjacent corner cutting edge increases. When such cutting insert is removably mounted onto an insert mounting seat of a tool body, an active cutting edge extends on a leading end side of the tool and an outer circumferential side of the tool, and one end surface relevant to this active cutting edge faces forward in a tool rotating direction and serves as a rake surface. At this time, the active corner cutting edge is located at the foremost position in the tool rotating direction in the active cutting edge, the active major cutting edge extends on the outer circumferential side of the tool body, and the active minor cutting edge extends on the leading end side of the tool. Accordingly, the active cutting edge is cut into a workpiece sequentially from the active corner cutting edge formed at the corner. When the active cutting edge is gradually cut into the workpiece from the corner cutting edge, a resistance applied instantaneously to the entire cutting edge is smaller as compared to a case in which the active corner cutting edge and the active major cutting edge as a whole are simultaneously cut into the workpiece, and the active cutting edge is advantageously resistant to fracture, etc.